A magneto-rheological fluid (MRF) is a smart material being developed. Under an applied magnetic field, solid magnetizable particles in a magneto-rheological fluid are in chainlike alignment with magnetic lines connected between the north pole and the south pole and thus produce resistance to a shear stress.
Although a conventional magneto-rheological fluid damper is advantageously characterized by controllability and swift changeability of the damping force, the prior art has its own drawbacks. The design of the magnetically permeable blocks and a single coil which are disposed inside the conventional magneto-rheological fluid damper leads to a relatively small area of the effective chaining taking place in magneto-rheological fluids and thereby results in a relatively small damping force. Also, when severed, the single coil causes a complete failure of the controllability of the damper and a great reduction in the damping force.
Referring to FIG. 1, there is shown a cross-sectional view of a conventional magneto-rheological fluid damper 9. As shown in the drawing, the magneto-rheological fluid damper 9 comprises a housing 91, a spindle 92, a damping block 93, a coil 94, and a magneto-rheological fluid 95. The spindle 92 and the damping block 93 are connected to each other and slidingly disposed in the housing 91. The coil 94 is wound around the damping block 93 to generate an applied magnetic field. The magneto-rheological fluid 95 is uniformly distributed in the gap between the damping block 93 and the housing 91.
Nonetheless, the damping block 93 and the housing 91 account for the area of the reach of the resistance force generated by the magneto-rheological fluid damper 9. A simulation clearly reveals that magnetic lines (as indicated by arrows shown in FIG. 1) pass mostly through small areas over and under the area of the reach of the resistance force, and in consequence the magnetic field at the central portion of the area of the reach of the resistance force is weak. Hence, the effective chaining of the magneto-rheological fluid 95 is limited mostly to the small areas over and under the area of the reach of the resistance force. The limited area of the effective chaining of the magneto-rheological fluid 95 results in the small area of the reach of a shear force arising from the magneto-rheological effect, thereby limiting the resistance force generated by the magneto-rheological fluid damper 9.
Furthermore, the performance of the magneto-rheological fluid damper 9 depends on the coil 94 which is wound around the damping block 93. Assuming that the coil 94 is damaged or severed, the coil 94 can no longer generate an applied magnetic field, thereby resulting in a complete failure of the damping force.
Accordingly, it is imperative to devise a magneto-rheological fluid damper which is effective in enlarging the area of magnetic permeability of a magneto-rheological fluid under an applied magnetic field to increase a damping force and preventing a complete failure of the damping force.